Brodix HVH Big-Block Heads - Head Games

Where smaller ports for your big-block really are better.

Years ago, performance of all sorts (Corvette and otherwise) was gained by "bigger equals better." It was more or less a sledgehammer approach to making things work. The bigger the sledgehammer, the better the Corvette ran. Or so we thought. Today, things are considerably different. Contemporary motorsports is a pretty good example of the "less is more" approach. After all, it's no secret that many forms of motorsports, even cars with restrictions (tires, induction, and so on) are becoming quicker and quicker on an almost daily basis. It's also no secret that in many cases camshaft profiles are shrinking, even in unlimited motorsports applications such as NHRA Pro Stock. Ditto with valve sizes. And right behind are cylinder heads with much smaller port sizes (and equally impressive flow numbers) than we once thought plausible. Case-in-point: Chevy's LS-series of engines. When enthusiasts first saw the new Corvette heads, eyes rolled. Heads (of the human variety) shook. Those itsy-bitsy ports would never work. Or so we thought. The small, raised ports on the LS-series engines move plenty of air. So much so, the less is more approach can be used on other Corvette engines.

A good example of this "smaller is really better" concept is the set of big-block Chevy heads shown in the accompanying photos. These heads are a collaboration between Brodix and Joe Petelle's High Velocity Heads (HVH), and they're easily capable of supporting 700-plus horsepower on pump gas (naturally aspirated). In practice, these heads have typically produced 1.69 hp per cubic inches on pump gas engines, ranging from 434 ci to 509 ci. As sold, this head design is equipped with 2.25-inch intake and 1.88-inch exhaust valves, both using 11/32-inch stems. The ports aren't big. In fact, they're downright tiny when compared to their contemporaries. The key to performance in these heads is the high-velocity design configuration that makes them ideal for both dedicated race cars and dual-duty (race and street) Corvettes.

When you think of port velocity and why it's important, you first have to think about the Bernoulli Principle. Daniel Bernoulli, a Swiss scientist from the 18th century, studied the relationship of fluid speed and pressure. When a fluid flows through a narrow constriction, the speed of the fluid increases. A good example is the speed of a river or creek when flowing through narrows. The fluid must speed up in the restricted region if the flow is to be continuous. Bernoulli observed that and wondered how the fluid gained the energy for the additional speed. He reasoned that the energy is acquired at the expense of a lowered internal pressure. His discovery-today referred to as Bernoulli's Principle-states: The pressure in a fluid decreases as the speed of the fluid increases.

Now, Mr. Bernoulli's Principle also applies to moving air. You can test it yourself by holding a sheet of paper in front of your mouth. When you blow across the top surface, the paper rises. This is because the moving air pushes against the top of the paper with less pressure than the air that pushes against the lower surface, which is at rest.

Keeping the Bernoulli Principle in mind, the velocity of a cylinder head port, coupled with impressive flow, is a target all of today's successful head porters shoot for. Some have a better handle on it than others. As an example, check out the flow numbers for the Brodix-HVH oval port big-block Chevy head chart.

It's easy to get big flow numbers with big ports, however, the port volume on the Brodix-HVH head is relatively small by comparison. The CNC-machined ports have an average volume of 301 cc's for the intake runner (keep in mind that a standard big-block Chevy head has slightly different runner sizes in stock form). How small are these ports? According to NHRA Blueprint Specifications, a stock '66 Corvette 425hp, 427 (L72) has an intake volume of 326 and 327 cc's, depending upon the head casting. A stock oval port GM head (for example, a '69 390hp 427) has a volume of 256 cc's.

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Brodix HVH Big-Block Heads - Head Games

The HVH CNC-machined intake port on the Brodix oval port head is relatively small-it has an average volume of 301 cc's. And that's a key to this head design: small port volume coupled with big flow numbers. As an example, this port moves over 373 cfm of air (at 28 inches) at 0.600-inch valve lift. Equally important is the fact that the head moves copious quantities of air throughout the valve lift range.

See the intake gasket template on the head? As you can see, the intake port on this head isn't in the stock location. The port is raised approximately 0.610 inches. The idea behind raising the port is to gain a line of sight shot straight to the valve. The port is also more or less the same shape at the gasket flange as a stock 1.85-inch by 2.16-inch port. The folks from Cometic have a dedicated intake gasket for this head.

The exhaust port on the Brodix-HVH head is also CNC-profiled. In this case, the exhaust port flows 267 cfm at 0.600-inch valve lift.

Like the intake side, the exhaust port is raised - this time 0.600-inch. And like the intake port, the idea is to get a straight shot from the valve to the exhaust header. The overall shape of the port is a modern "squashed" D-port. A common Fel Pro exhaust gasket can be used.

With the head flipped over, you can see that the Brodix-HVH head incorporates a fully machined, heart-shaped combustion chamber. The chamber volume will measure (approximately) 110 cc's, depending upon the valves, and can be used with open-chamber configuration pistons.

The chamber makes use of a 14mm by 3/4-inch reach gasketed spark plug. Because the spark plug location is revised from the OEM Chevy design, Brodix recommends that you positively check spark plug to piston dome clearance.

These CNC-ported big-block heads are available with and without valves. In this case, the heads shown do not include valves, however, the heads are sized for 2.25-inch intake and 1.88-inch exhausts. Intake valves with a 0.250-inch longer stem length and stock stem length exhausts are recommended. Note the bronze guides. The heads are engineered to accept 11/32-inch stem diameter valves.

Valvespring pockets on the Brodix-HVH big-block head are machined to accept 1.540-inch-diameter springs. Typically, the head can be machined for a larger 1.626-inch-diameter spring, as long as the pocket depth is not increased.

The bowl area of the Brodix-HVH head has seen a considerable amount of CNC-machining, on both the intake and the exhaust side (the bowl of the cylinder head is the area of the port immediately behind the valve head). The bowls in most cylinder heads are bored with a vertical mill.

Typically, this leaves a sharp transition to the balance of the port, which in turn can create turbulence and port restrictions. Proper modifications to the bowl area (such as this) can contribute to as much as 35 percent of the total flow of the port.

The cylinder head will accept a conventional roller rocker assembly, using an equally conventional 7/16-inch rocker stud. It can also accept a shaft rocker setup (for example, Jesel). Be sure to specify a rocker for a Brodix -2 head.

Brodix casts the heads at their own foundry, using 356 aluminum, and then heat-treats them to a T6 condition. Race heads such as this are designed with revised spark plug locations, and incorporate decks with a minimum thickness of approximately 9/16-inch. This provides ample room to mill the heads (and consequently reduce the chamber volume).

Read about Brodix all new 229 small-block oval port cylinder heads and how they can benefit you. Only at www.chevyhiperformance.com, the official website for Chevy High Performance Magazine! » Read More